Bone conduction is the conduction of sound to the inner ear through the bones of the skull, and a bone conduction hearing aid, or bone conductor, is a device that stimulates through bone conduction. Other types of hearing aids may instead directly stimulate the tympanic membrane, the middle ear ossicles, the round window, the oval window or the cochlear fluid. Several different types of bone conduction hearing aids are available. A bone conduction hearing aid may amplify sound or it may also work as a tinnitus masker. A bone conductor may also be used in audiometry to determine bone conduction hearing thresholds. Current bone conductors include however several drawbacks, as described below.
The traditional bone conductor consists of a hearing aid with a vibrator that is pressed against the head behind the ear by a spring arrangement extending from the other side of the head. The steel spring arrangement is sometimes built into an eyeglass frame. The vibrations are transmitted through the skin and the skull bone into the inner ear. For the traditional bone conductors with a spring arrangement around the head, the constant pressure against the skull bone often causes headaches and skin irritation. The spring arrangement is also bulky and is not a practical or user friendly solution.
Another type of established bone conductor, which is sometimes called a direct bone conductor, includes a vibrator, which is directly and firmly connected to an anchoring component that is anchored to the skull bone through which the vibrations are directly transmitted from the vibrator to the skull bone. The vibrations do not pass through the skin on its way from the vibrator to the skull bone. This type of bone conductor may be designed with a permanent skin penetration which may lead to problems with skin infections. If this type of bone conductor is instead designed with an implanted vibrator and where energy are transmitted from an external hearing aid there is a significant energy loss when transmitting the energy with an inductive link through the skin. Another drawback is that the vibrator cannot easily be repaired if it breaks down.
Another type of bone conductor is a type where the vibrator is placed in an external unit outside the skin and where this external unit is kept in place through a magnetic attachment to a part that is anchored to the skull bone and implanted under the skin. In this arrangement, the signal from the external part is passing through the skin to the implanted part and the skull bone. For this type of bone conductor, surgery is still required and the magnetic force may cause skin necrosis due to the constant pressure against the skin and the hearing aid may also easily fall off.
JP 201 1087142 (A) presents a solution where a vibrator is attached to the skin of a user by means of an adhesive sheet. Although JP 201 1087142 (A) reduces the pressure against the head, it is still in need of further improvements in terms of functionality and comfort.
There is a need for a more effective bone conduction hearing aid system that is reliable and does not have the drawbacks discussed above.